Basic investigations as to the structure and function of the beta-galactoside binding protein, or lectin, of rat lung are proposed. The lectin is presently determined by its ability to agglutinate erythrocytes through an interaction with their oligosaccharide cell surface determinants. Other mammalian lectins with similar properties have been postulated to function in cellular recognition, adhesion and developmental processes. Within the rat, lectin is specifically abundant in heart and lung. However, neonatal lung contains no active lectin; activity appears to peak sharply at about day 13 before declining slowly. Lectin has been purified from rat lung. Anti-lectin antibodies will be raised in rabbits and fluorescently labelled for use in immunofluorescence studies to localize the lectin. A specific binding assay for the lectin will be developed. Biochemical methods will be used to investigate the native molecular form of the lectin and the number and specificity of the saccharide binding sites. A profile of rat lung lectin activity with postnatal age will be obtained and correlated with the morphological changes associated with postnatal lung development. Together these studies should afford exciting information pertinent to the design of a hypothesis as to the role of lectin in lung function.